The present invention relates to apparatuses, methods, and programs for image processing. Specifically, this invention relates to those which can make printouts (hard copies) of stable densities from diagnostic image data.
As an image processing apparatus containing a densitometer, a digital laser imaging system (hereinafter referred to as an imager) equipped with a densitometer has been known as described, for example, in Patent Document 1. The densitometer in the imager is used to control the gradation characteristics of the imager and the final film (hard copy) density. For example, the built-in densitometer is used to measure the densities of patches which are recorded on a prescribed position of a film in order to control image densities by the so-called calibration process which includes the steps of exposing the film to form a latent image of multiple step wedges by prescribed exposure signals, developing the film to make the latent image visible, measuring the final density of each of the step wedges, and creating a look-up table (LUT) which determines exposure amount for inputted diagnostic image data to optimize the final film gradation characteristics from the result of this measurement, or by the feedback correction processing (FB correction processing) which determines the feedback correction values to optimize the image density of the next film.
When a hospital has two or more imagers, an external standard densitometer, in addition to the built-in densitometer of respective imagers, is generally used to manage the print densities of the imagers to check whether the final print densities are within the predetermined allowable range. In other words, the resulting density graduations controlled according to the result of measurement by the built-in densitometers in the imagers are compared with the final film density gradations measured by this external standard densitometer to check whether the density gradations are in the predetermined allowable range.
If the density gradations are not in the predetermined allowable range, the densitometers must be corrected to eliminate the difference in readouts between the built-in densitometers and the external standard densitometer. Specifically, it is common to measure the densities of the printed film by the external standard densitometer, to compare the readouts between the built-in densitometers and the external standard densitometer, and to correct the values measured by the built-in densitometers to eliminate the difference between the readouts. This correction is made because, if the readouts between the external standard densitometer and the built-in densitometer of an imager are kept different while the image density is constant, the respective imagers produce films of different image densities after exposure and development processes in the patch density control (patch feedback) system (hereinafter, referred to as the FB correction) and this may cause management problems.
The FB correction controls film densities by forming a rectangular area (patch area) of about 5×10 mm on a prescribed location of each film with a prescribed exposure amount, measuring its finished density, comparing the measured density value with a target density value, and controlling the exposing and/or developing conditions to optimize the density of the subsequent film according to the difference.
In the FB correction using the density of the above rectangular area measured by the external standard densitometer, when the target density is 2.0, based on the measured density (of 1.9 for example), the density control can be effective by correcting to eliminate this difference (0.1=2.0−1.9)(the density of the subsequent film is increased by +0.1). However, in the FB correction using the density of the above rectangular area measured by the built-in densitometer, if the readout of the built-in densitometer is 2.0 due to an error even though the readout of the external standard densitometer is 1.9, the density correction is not carried out if the target density is set as 2.0, and the effective density control will not be carried out.
Imagers of the heat development type which are described in Patent Document 2 have been popular as imagers each of which houses a densitometer. This type of imager develops a film to make the latent image visible by heating while conveying the film. Therefore, a built-in densitometer on the downstream side of the heat developing section tends to be thermally affected by hot films. Further, when the densitometer is housed in a downsized imager which has been desired recently, the densitometer is also thermally affected by the heating means directly. Therefore, the built-in densitometer must be thermally stable in a wide temperature range. If this thermal characteristic is not satisfied, the finished film density may be affected.
The thermal errors of such a densitometer may be suppressed when its components have good temperature characteristics. However, such components may increase the component cost. A cooling fan can be one of good methods for suppressing thermal influence on the built-in densitometer by keeping the surrounding temperature within a predetermined temperature range, but it occupies a space in the imager and increases cost. Although a cooling fan can reduce the thermal influence on a densitometer to some degree, the densitometer cannot substantially be free from thermal influence.    [Patent Document 1] Tokkai Hei 6-233134    [Patent Document 2] Tokuhyou Hei 10-500497
After the above problems were carefully studied and researched, it was found that stable image densities could be obtained without frequent calibrations of built-in densitometer by measuring densities at various temperatures by the respective built-in densitometers, creating a characteristics variation table of each built-in densitometer based on the measured density values, and correcting the values measured by the densitometer after the calibration of the densitometer according to the characteristics variation table of the densitometer, which has led to the present invention.
An object of the present invention is to provide apparatuses, methods, and programs for image processing which can make film sheets of stable image densities without measurement errors of a built-in densitometer caused by thermal variations.